The present invention relates to a magnetoresistance effect type head which detects the intensity of a magnetic field by utilizing a change in resistance corresponding to the intensity of the magnetic field and to an information reproducing device which reproduces the information stored in a storage medium.
Recently, along with recent spread of computers, a lot of information has been handled daily. Such information is stored in a storage medium by a large number of physical signs such as directions of magnetization or the presence/absence of pits and reproduced by an information reproducing device which reads these signs and converts these signs into electric reproducing signals corresponding to the state of these signs.
Storage mediums which store information in the form of the direction of magnetization include magnetic disks. The magnetic disk is provided with a surface which is made of a magnetic material and divided into a large number of fine one-bit areas which are respectively magnetized, and stores one-bit information in each one-bit area in accordance with the direction of magnetization. A hard disk drive which is an information reproducing device for regenerating the information stored in the magnetic disk is provided with a reproducing magnetic head for detecting an external magnetic field. This reproducing magnetic head is located so as to be close to or in contact with each of one-bit area of the magnetic disk and creates electrical reproducing signals corresponding to magnetic fields generated by the magnetization of these one-bit areas to thereby reproduce the information stored in the above magnetic disk.
The memory density of information stored in the magnetic disk is raised every year. Along with the rise in the memory density, the area occupied by the one-bit area of the magnetic disk is decreased. As the reproducing magnetic head, a highly sensitive one is required to detect the direction of the magnetization of the one-bit area decreased in the area.
As the highly sensitive reproducing magnetic head, a magnetoresistance effect type head is known which utilizes a magnetoresistance effect that the resistance changes corresponding to external magnetic fields. Among these magnetoresistance effect type heads, a spin valve head is known as a particularly highly sensitive head. This spin valve head comprises a multilayer film containing a free magnetic layer which changes in the direction of magnetization corresponding to external magnetic fields and produces a large change in resistance by the change in the direction of magnetization. This spin valve head uses the section of the above multilayer film as an information reading section, which is made to be close to or in contact with each one-bit area of the magnetic disk, to create electrical reproducing signals by utilizing a change in resistance corresponding to the magnetic fields produced by the magnetization of the one-bit area.
This free magnetic layer of the multilayer film tends to produce a magnetic wall at the end portions. If this magnetic wall is moved due to a change in external magnetic fields, the above reproducing signals generate a Barkhausen noise along with the movement of the magnetic wall. In order to suppress the generation of this Barkhausen noise, a magnetic wall control layer comprising a hard magnetic ferromagnetic material or the like is disposed as a part layer of the above multilayer film and a static magnetic field is applied to and exchange interactions are exerted on the free magnetic layer by the magnetic wall control layer to thereby fix the magnetic wall. However, it is required for the magnetic wall control layer to have a thickness equal to or larger than a predetermined thickness to suppress the generation of the Barkhausen noise sufficiently.
However, the spin valve head has the problem that if the magnetic wall control layer is thick, the thickness of the multilayer film constituting the spin valve head is increased and the width of the reading section using the section of the multilayer is widened, with the result that it is difficult to effectively detect the magnetic field generated by the magnetization of the one-bit area having a small area in the magnetic disk having high memory density.
In view of the above situation, it is an object of the present invention to provide a magnetoresistance effect type head and an information reproducing device which well reproduces the information stored in a storage medium with high memory density while limiting the generation of Barkhausen noises.
A magnetoresistance effect type head according to the present invention which attains above object, comprises:
a magnetoresistance effect element which is changed in resistance corresponding to the intensity of an external magnetic field, and the step of detecting the intensity of a magnetic field by detecting the magnitude of the resistance of the magnetoresistance effect element,
the magnetoresistance effect element comprising a multilayer film containing a free magnetic layer which is changed in the direction of magnetization corresponding to an external magnetic field, wherein the free magnetic layer is provided with an overhang portion which is overhung and spread from a layer excluding the free magnetic layer and constituting the multilayer film, and
paired magnetic wall control layers which are in contact with the top and under surfaces of the overhang portion of the free magnetic layer respectively and restrict the movement of the magnetic wall of the overhang portion.
In the magnetoresistance effect type head of the present invention, the magnetic wall control layer preferably comprises any one of materials selected from the group comprising a hard magnetic ferromagnetic material and a hard magnetic antiferromagnetic material.
The magnetoresistance effect type head is provided with the paired magnetic wall control layers which are in contact with the top and under surfaces of the overhang portion of the free magnetic layer respectively and restrict the movement of the magnetic wall of the overhang portion. Therefore, a static magnetic field is applied to the free magnetic layer from both the top and under surfaces, and the area where the magnetic wall control layer and free magnetic layer are in contact with each other is large, and further, exchange interactions are exerted on many parts between the both layers. As a result, the movement of the magnetic wall in the free magnetic layer is limited more efficiently, giving difficulty in the generation of Barkhausen noises. Therefore, the width of a reading section which reads the information of a storage medium can be narrowed by thinning the magnetic wall control layer with keeping the function for limiting the generation of Barkhausen noises. For this reason, this magnetoresistance effect type head is suitable as a head regenerating the information of a storage medium which information is stored at high density.
In the magnetoresistance effect type head of the present invention, preferably the free magnetic layer is arranged as the lowermost layer among the multilayer film constituting the magnetoresistance effect element and comprises:
an intermediate layer having the same altitude as the magnetic wall control layer, which is formed on the lower layer side of the overhang portion among the paired magnet wall control layers, on the side of a lower layer of a portion other than the overhang portion, and
an electrode on the upper layer of the magnetic wall control layer formed on the upper layer side of the overhang portion for flowing current through the magnetoresistance effect element.
Generally, a dielectric layer is formed on the above electrode and magnetoresistance effect element of the magnetoresistance effect type head and a conductive magnetic shield layer is formed on the dielectric film.
Since this magnetoresistance effect type head is provided with the intermediate layer, a difference in level between the electrode and the magnetoresistance effect element is small. When the difference in level is large, the electrode becomes close to the magnetic shield layer at the step. On the contrary, since the difference in level is small in this manner, the electrode and the magnetic shield layer in this magnetoresistance effect type head is far apart at an interval equal to or larger than a predetermined distance and insulation between the electrode and the magnetic shield layer is therefore secured.
Moreover, in the magnetoresistance effect type head of the present invention, the intermediate layer preferably comprises one or more materials selected from the group comprising Ta, Cr, TiW, Al2O3 and AlN.
Among these materials, since Ta imparts high crystallinity to the free magnetic layer, it is preferable as the material for the intermediate layer, since Cr and TiW impart high crystallinity to the magnetic wall control layer which is disposed adjacent to the intermediate layer and is occasionally overlapped on both end portions of the intermediate layer, they are preferable as the material for the intermediate layer and Al2O3 and AlN have insulation high enough to prevent the leakage of current from the free magnetic layer and are hence preferable as the material for the intermediate layer.
An information reproducing device according to the present invention which attains above object, comprises:
a magnetic head which is disposed close to or in contact with a magnetic storage medium in which information is stored by magnetization and detects the magnetization of each point of the magnetic storage medium, and the step of reproducing information corresponding to the magnetization of each point of the magnetic storage medium which magnetization is detected by the magnetic head,
the magnetic head comprising a magnetoresistance effect element which is changed in resistance corresponding to the intensity of an external magnetic field, and detecting magnetic field signals by a change in the resistance of the magnetoresistance effect element,
the magnetoresistance effect element comprising a multilayer film containing a free magnetic layer which is changed in the direction of magnetization corresponding to an external magnetic field, wherein the free magnetic layer is provided with an overhang portion which is overhung and spread from a layer, other than the free magnetic layer, constituting the multilayer film; and
paired magnetic wall control layers which are in contact with the top and under surfaces of the overhang portion of the free magnetic layer respectively and restrict the movement of the magnetic wall of the overhang portion.
This information reproducing device comprises a magnetic head comprising the paired magnetic wall control layers which are in contact with the top and under surfaces of the overhang portion of the free magnetic layer respectively and restrict the movement of the magnetic wall of the overhang portion similarly to the above magnetoresistance effect head. Therefore, the information reproducing device is suitable as a device for reproducing the information of the storage medium which information is stored at high density.
As explained above, the present invention can provide a magnetoresistance effect type head and an information reproducing device which well reproduces the information stored in a storage medium at high memory density while limiting the generation of Barkhausen noises.